Ultrafast Photoinduced Symmetry-Breaking Charge Separation and Electron Sharing in Perylenediimide Molecular Triangles

By Wu, Yilei; Young, Ryan M.; Frasconi, Marco; Schneebeli, Severin T.; Spenst, Peter; Gardner, Daniel M.; Brown, Kristen E.; Wurthner, Frank; Stoddart, J. Fraser & Wasielewski, Michael R.
Published in Journal of the American Chemical Society NULL 2015

Abstract

We report on a visible-light-absorbing chiral molecular triangle composed of three covalently linked 1,6,7,12-tetra(phenoxy)perylene-3,4:9,10-bis(dicarboximide) (PDI) units. The rigid triangular architecture reduces the electronic coupling between the PDIs, so ultrafast symmetry-breaking charge separation is kinetically favored over intramolecular excimer formation, as revealed by femtosecond transient absorption spectroscopy. Photoexcitation of the PDI triangle dissolved in CH?Cl2 gives PDI+•-PDI-• in τCS = 12.0 ± 0.2 ps. Fast subsequent intramolecular electron/hole hopping can equilibrate the six possible energetically degenerate ion-pair states, as suggested by electron paramagnetic resonance/electron-nuclear double resonance spectroscopy, which shows that one-electron reduction of the PDI triangle results in complete electron sharing among the three PDIs. Charge recombination of PDI+•-PDI-• to the ground state occurs in τCR = 1.12 ± 0.01 ns with no evidence of triplet excited state formation.

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